Retinoids are potent inhibitors of the induction of ornithine decarboxylase (ODC) and increased rRNA synthesis elicited by tumor promoters, carcinogens or cell cycle traverse in ertain cell types. The mechanism of tetinoid action is unknown. It is also unknown whether retinoid inhibition of these intracellular processes is the primary site of action by which the retinoids cause inhibition of the cellular events of tumor promotion and formation and cell proliferation. The aims of this project are: (1) to determine the molecular mechanims(s) that account for the action of retinoids to inhibit ODC induction and increased rRNA synthesis during G1- progression of CHO cells and 920 to determine whether retinoid inhibition of these intracellular events is the cause of the retinoid-induced g1-phase proliferative arrest. The first aim will be accomplished by a combined biochemical and immunochemical approach. Antibodies to ODC will be used to test the effect of retinoids on the cellular content of active and inactive ODC, the turnover of the enzyme, and the cellular level of translatable mRNA for ODC. Nuclei will be isolated from proliferating and retinol-arrested cells and differences in content of RNA polymerase I and the putrescine-conjugatd activator protein for the biosynthetic enzyme assessed. The action of retinoids to limit production ofthe activator protein by inhibiting the nuclear-associated transglutaminase will be examined at the level of cellular lipid metabolism, to determine if retinoids block production of the specific phospholipid metabolite(s) required to support enzyme activity at physiological CaZ+ concentrations. The second aim will be accomplished by cellular reconstitution experiments. Increased levels of ODC and RNA polymerase I activator protein will be restored in retinol-arrested cells by microinjection or liposome fusion of the purified proteins. The effect of reconstitution on relieving the retinoid induced G1 proliferative arrest will be measured by time lapse video microscopy and fluorescence-activated cell sorting. These studies should yield new information regarding the molecular mechanisms by which retinoids act to alter intracellular events and the functional consequences of this action to the cellular processes of cell growth and carcinogenesis.